I. Field of the Invention
The present invention relates to a mechanical part having a wear-resistant surface and cosisting of a non-ferrous metal.
II. Description of the Prior Art
Aluminum is light in weight, has a good corrosion resistance in, air and high electrical and thermal conductivities, and can be easily machined. An aluminum alloy is obtained by adding various elements to aluminum, so as to improve its characteristics for application in various fields. Aluminum and aluminum alloy having the above characteristics are widely used as a material for chemical industry devices, electrical instruments, optical instruments, sanitary vessels, buildings, ships, vehicles, household articles, and the like.
On the other hand, nickel is superior both in heat resistance and corrosion resistance, and hence is used as a material, in the form of a plate or a bar, by food industries, chemical industries, electrical instruments, and the like. A nickel alloy is obtained by adding various elements to nickel, so as to improve its characteristics, and is used as a heat-resistant material, a corrosion-resistant material, and a magnetic material.
Aluminum, aluminum alloy, nickel, and nickel alloy are also widely used respectively as a material for a mechanical part such as a roller which is brought into contact with running paper, a plastic film, a fibrous member, and the like, and for a mechanical part such as a bearing part or a sliding part which is brought into contact with another mechanical part. In these cases, in order to prevent wear on the surface and to improve its sliding property in relation to another part, superior wear resistance and superior surface smoothness are required. Such a mechanical part which produces friction between itself and another member must be made of a material selected in accordance with its required characteristic, and must be able to maintain this characteristic at high level.
In addition, aluminum and aluminum alloy are widely used in chemical plants, and nickel and nickel alloy are widely used as a shaft or an impeller of a pump. However, these parts are mainly used in a corrosive atmosphere such as watr, acid, or alkali, and hence require good corrosion resistance. A part used in such a corrosive atmosphere must be made of properly selected material which has and is able to maintain a high level of corrosion resistance.
In recent years, attempts have been made to form a surface layer which is different from a substrate, on the surface of parts, so as to endow parts consisting of aluminum, aluminum alloy, nickel, or nickel alloy, in with the characteristics required according to conditions of use or environmental factors, addition to their original characteristics. Such a surface layer must have satisfactory wear resistance to friction produced in association with other parts, as well as a high degree of smoothness for improving its sliding properties in relation to other parts, must not damage other parts, and must have a sufficiently high resistance to chemicals, so as not to become corroded in a corrosive environment. Furthermore, the surface layer formed on the substrate surface of the parts must have high mechanical strength, must not degrade the characteristics of the substrate upon formation, and require no finishing such as grinding after formation.
Known methods for forming a surface layer on a substrate surface of parts consisting of aluminum, aluminum alloy, nickel, or nickel alloy plating, are PVD (physical vapor deposition), CVD (chemical vapor deposition), frame spraying, and the like. However, these methods cannot always satisfy all the above-mentioned requirements, and practical application is not easily accomplished. More specifically, surface layers formed by these methods have insufficient density, wear-resistance, and smoothness. The bonding strength between the surface layer and the substrate is also insufficient, and the surface layer often peels away from the substrate. In addition, a finishing process is required after the formation of the surface layer.